1. Field of the Invention
This invention relates to apparatus for simultaneously varying the pitch of a plurality of fan blades of a fan assembly forming a part of an induced draft water cooling tower or the like. Typically, such fans may have an overall diameter as great as 10 meters.
2. Information Disclosure Statement
Industrial water cooling towers serve the purpose of reliably providing cooling water to process equipment or power plant steam condensers at specified cold water temperatures under widely varying ambient temperature and relative humidity conditions. Since the cost of operating cooling towers has become a much more critical design factor in recent years because of energy costs including expenses associated with fan motor operation, more emphasis is now being given to ways to economically assure flow of adequate air through a particular tower design.
In order to effectively control the temperature of cold water from the tower and particularly to maintain such temperature at least as low as prescribed by the user, various operating parameters of the tower or process have been monitored and the data usually used to control fan operation. Efforts have centered on use of controllers functional to turn fans on or off, change the speed of the fans, or vary the pitch of the fan blades. Sensing units have been provided to measure air, water or process temperatures. The values obtained are then employed to control fan operations. Certain prior designs involved two-speed fan motors giving the operator a choice between off, low speed or high speed fan rotation. There are advantages from an initial cost as well as operating efficiency to the use of variable pitch fan blade units, but design problems have impeded more widespread adoption of variable pitch fan blade systems in the cooling tower industry.
One deterrent has been the rather hostile environment in which the assembly must operate. Warm moist air is present on a continuous basis. Users often add agents to the water to control algae and fungus. Icing can occur in extremely cold weather. Galvanic corrosion may be a factor from the use of dissimilar metals. Minerals in the water can accumulate on the fan components.
One variable pitch fan blade unit which has found some success was placed in use by the assignee hereof some time ago. This unit employed a constant speed electric motor for driving a variable pitch fan. A temperature sensitive controller was used to control supply of pressurized fluid to the unit for varying the pitch of the blades to maintain a required cold water temperature. This assembly had a centrally compression spring within an enclosure which extended upwardly from the fan housing for biasing a hub within the housing in opposition to pressurized fluid directed to the unit. While this device overcame many of the problems encountered with the control and operation of cooling tower fans and utilized a relatively economical constant speed motor, the unit was not acceptable in many applications because of the height of the assembly. The increased height of the fan hub assembly including the compression spring and a centrally located actuating mechanism raised the overall height of the fan and therefore required a substantially higher fan cylinder.
A need has therefore existed in the art for variable pitch fan apparatus of the type described hereinbefore but having a compact overall height accomplished by telescoping blade pitch mechanism over the fan shaft so that the fan assembly may be installed within existing cooling towers without the need for increasing the overall height of the fan cylinder.